The present invention relates generally to a chemical vapor deposition (CVD) apparatus. More particularly, improvements to a gas manifold of a CVD apparatus, and a method for testing a seal of a CVD apparatus gas manifold for leaks are disclosed.
Chemical vapor deposition (CVD) apparatus are known for use in the fabrication of integrated circuit chips. CVD apparatus in particular are used for depositing layers of certain materials such as polysilicon, tungsten, and silicon nitride on a semiconductor wafer substrate. In the CVD process, gaseous reactants chemically react to deposit individual atoms of a particular element or elements on the wafer surface. The deposition reaction occurs in a hermetically sealed chamber in which the wafer substrate is placed. The gaseous reactants are first fed through a gas manifold arranged outside the sealed chamber, and then from the gas manifold into the sealed chamber.
FIGS. 1 and 2 illustrate a gas manifold 10 of a conventional CVD reactor, such as the P-5000 available from Applied Materials, Inc. of Santa Clara, Calif. Gas manifold 10 includes a quartz gas feed tube housing 12, a gas feed endblock 14, and a gas inject endblock 16. Endblocks 14 and 16 are connected to a gas chamber lid 18 of the CVD reactor. The CVD reactor further includes a cooling water manifold 20 and cooling water endblock 22. Gaseous reactants are fed first through the lower end of gas feed endblock 14, then through housing 12, through gas inject endblock 16, and finally through a mixer gas box 24 arranged in the sealed chamber of the CVD apparatus.
FIG. 2 shows the assembly of the various parts of gas manifold 10. O-ring kalrez gaskets 26 are arranged in respective gas flow ports of endblocks 14 and 16. Metal spacers 28 and spring wave washers 30 are interposed between gaskets 26 and quartz gas feed tubes 32, which are fit in ceramic resistors 34 and housed in housing 12. Screw and washer assemblies 36 are used to connect endblocks 14 and 16 to housing 12, so that gaskets 26 provide sealed gas flow paths extending through respective aligned gas flow ports of housing 12 and endblocks 14 and 16. O-ring vitton gaskets 38 are also arranged about both of the gas flow paths shown.
Gas manifold 10 must be frequently checked for leaks. Leaks can introduce oxygen into the CVD apparatus and thereby damage wafers and/or the apparatus itself. Large leaks can quickly do substantial damage, but are rather easy to detect. Microleaks, which often occur at seals on the gas flow path, can also do substantial damage and, in addition, can be quite difficult to detect. In the system shown in FIG. 2, a gas leakcheck hole 40, normally closed by seal plug 42, is provided for this purpose. Gas leakcheck hole 40 extends in gas feed endblock 14, from an upper surface thereof to a surface thereof which engages with a surface of housing 12. Leak checking is performed by drawing a vacuum in the sealed chamber of the CVD apparatus, feeding a leak check gas such as helium into the gas leakcheck hole 40, and determining, with a conventional gas detection apparatus, whether the leakcheck gas has entered into the sealed chamber. The presence of leakcheck gas in sealed chamber would indicate that helium has entered through a leak in gas manifold assembly 10.
A particular problem observed with conventional CVD apparatus gas manifolds is that the leakcheck gas may not detect microleaks in the various seals along the gas flow paths. It has even been observed that microleaks in the seals between gas feed endblock 14 and quartz feed tube housing 12 are frequently missed by leak checking through leakcheck hole 40. This problem arises because the leakcheck gas has no clear path to the potentially leaking seals. In some cases, it happens that the leakcheck gas is detected in the sealed vacuum chamber, however in such a small amount, or with a "weak" indication, which could lead to uncertainty as to whether or not the gas manifold assembly has a defective seal. Additionally, it may happen that a strong indication of leakcheck gas in the vacuum chamber is detected, however the leakcheck operator is given no indication as to which of the many seals in the gas manifold is defective.